1. Field of the Invention
This invention relates generally to a valve system of a four cycle engine and more particularly to an engine decompression system for the valve system.
2. Description of the Related Art
Many four cycle engines include a decompression system to make starting the engine easier. Such decompression systems are desired because of the high compression ratios that are often used in four-cycle engines. The high compression ratios produce large compression forces that must be overcome by an operator or a starter motor to start the engine. The decompression system reduces these forces by opening the exhaust valves and thereby effectively reducing the compression ratio when starting the engine.
There are several types of decompression systems. See, e.g., U.S. Pat. Nos. 4,369,741, 5,816,208 and 6,343,579. In U.S. Pat. No. 5,816,208, the decompression system includes a decompression actuating shaft that is inserted into a bore formed within a camshaft. The decompression actuating shaft actuates pins that are moveably positioned within pinholes positioned within the camshaft. When actuated by the decompression actuating shaft, the pins lift the exhaust valves to reduce the compression ration.
A need exists for an improved decompression system that is easy to manufacture and assemble and is also reliable. In particular, in engines with multiple cylinders (e.g., three or more), the camshaft and decompression actuating shaft become increasingly long. This tends to increase the difficult and costs of manufacture and assembly and to reduce reliability.
In one embodiment of the present invention, a decompression system for a four-cycle engine comprises a camshaft, decompression shaft, and at least one decompression pin. The camshaft has at least one cam arranged to activate a valve of the engine and an internal bore that extends generally longitudinally with respect to the camshaft. The camshaft also includes at least one pin hole arranged generally perpendicular to the internal bore. The decompression shaft comprises a first longitudinal portion and a second longitudinal portion that are configured to fit within the internal bore of the camshaft. The decompression shaft is moveable between a first position and a second position and further comprises at least one cam surface having a first portion and a second portion. The cam surface is arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve.
In another aspect of the present invention, a method of assembling a decompression system for an engine comprising forming a bore within the camshaft, the bore having a middle portion with a first diameter and a second portion with a second diameter that is larger than the first diameter, forming at least one pin hole in the camshaft, the pin hole extending generally perpendicular to a longitudinal axis of the camshaft, inserting a pin into the pin hole, forming a first portion of a decompression shaft, forming a second portion of a decompression shaft, and inserting the first portion and second portions of the decompression shaft into the bore.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.